氟硼二吡咯类pH荧光探针PET光谱特性的理论计算

氟硼二吡咯(BODIPY)类pH荧光探针分子是基于光诱导电子转移(PET)的荧光探针分子, 识别基团氮原子上引入不同取代基可呈现不同的光学灵敏度. 本文应用密度泛函理论(DFT)及含时密度泛函理论(TD-DFT)方法对六种含不同取代基的探针分子进行了几何构型优化及激发态计算, 探讨了不同取代基对PET效应影响. 计算结果表明: 基态时这些探针分子的最高占有分子轨道(HOMO)和最低未占有分子轨道(LUMO)都在荧光母体BODIPY的π, π^*轨道, 而识别基团上氮原子孤对电子所在的轨道为HOMO-1轨道. 但是在激发态, 当氮原子上有两个取代基时, HOMO-1→LUMO跃迁的激发能都小于荧光团的HOMO→LUMO跃迁, 这将有可能产生PET效应并导致荧光熄灭, 而当氮原子上有一个取代基时不会出现这种现象. 通过激发态结构优化可以发现, 无论识别基团氮原子上有一个还是两个取代基, N原子的轨道对称性都发生变化, 由sp³→sp², 孤对电子占据在p轨道上, 其轨道能级升高至荧光团的HOMO和LUMO轨道之间, 将导致不同程度的PET效应, 与实验结果一致.     

8-羟基喹啉银(铂)金属配合物电子光谱与非线性光学性质

运用密度泛函理论B3LYP方法对8-羟基喹啉(银、铂)(AgQ、PtQ₂)金属配合物及其衍生物的非线性光学性质进行理论计算研究. 结果表明: 引入取代基使铂配合物的最强吸收波长产生较大红移. 最低能量跃迁吸收来自最高占据分子轨道(HOMO)到最低空分子轨道(LUMO)的d→π^*和π→π^*跃迁, 属于金属配体电荷转移(MLCT)与配体配体电荷转移(LLCT). 金属银和铂掺杂8-羟基喹啉使其三阶非线性光学系数γ值明显增大, 并且在配合物上引入―Ph, ―PhOCH₃, ―PhF₂, ―PhF₅基团将进一步增大γ值. 引入基团的供电子性越强, γ值增大的幅度越大, 引入基团的吸电子性越强, γ值增大的幅度越小.     

三核金配合物分子间Au-Au相互作用及其发光性质的含时密度泛函理论研究

使用混合密度泛函方法(MPW1PW91交换相关势), 对Au₃(HOC＝NH)₃分子进行了几何构型全优化, 在此基础上构建了Au₃(HOC＝NH)₃二聚体和三聚体模型, 采用含时密度泛函方法研究了单体和低聚体模型的分子间Au-Au相互作用与其发光性质的关系. 计算结果表明: 此d¹⁰亚金化合物低能激发态的主要成分是反键或非键的Au(5d)电子轨道到前线附近Au(6p)空轨道的跃迁, 并且这种激发大大加强了分子间Au-Au相互作用, 从而形成激发多聚体, 导致这类化合物溶液或固体发射谱红移.     

1-甲基胸腺嘧啶A-带结构动力学

获取了1-甲基胸腺嘧啶(MT)涵盖紫外光谱中A带和B带吸收的共5 个激发波长的共振拉曼光谱, 并结合密度泛函理论方法研究了MT的电子激发和Franck-Condon 区域结构动力学. 在TD-B3LYP/6-311++G(d,p)计算水平下, A带和B带吸收被分别指认为π_H→π_L^*/π_H-2→π_L+2^*和π_H→π_L+2^→/π_H-2→π_L^*跃迁. 甲基参与嘧啶环的共轭使MT的A带最大吸收波长λ_max相对于胸腺嘧啶(T)发生明显红移, 并对Franck-Condon区域的动态结构产生一定影响. A带和B带共振拉曼光谱分别被指认为14 个振动模式和11 个振动模式的基频、泛频和组合频. C5＝C6伸缩+C6H12面内弯曲振动v₉, 环变形振动v₁₆和N3C2N1反对称伸缩+C4C5C10反对称伸缩振动v₁₈占据了A带共振拉曼光谱强度的绝大部分. 这表明¹π_Hπ_L^*激发态结构动力学主要沿这些反应坐标展开. 考察了溶剂对共振拉曼光谱的影响, 结果表明, C4＝O9伸缩+N3H11面内弯曲振动v₈的活性与溶剂性质有关, 其激发态位移量随溶剂性质的变化规律与胸腺嘧啶一致.     

含噻吩环的吡啶Ru(II)配合物的电子结构和非线性光学性质

采用密度泛函理论(DFT) B3LYP方法对含有噻吩环的吡啶Ru(II)配合物的电子结构和非线性光学(NLO)性质进行理论研究. 结果表明: 配合物[Ru^II(NH₃)₅L]²⁺(L为含噻吩环的有机基团)中, 配位原子与中心金属离子间没有形成稳定的化学键, 但存在较强的供体-受体(D-A)相互作用; NH₃被羰基(CO)取代后, Ru-C间形成了稳定的σ-π配键, 降低了受体的空轨道能级. 噻吩环的增加增大了体系的共轭程度, 有利于分子内电荷转移, 使配合物的极化率α和一阶超极化率β明显增加. 结合配合物的前线分子轨道分析发现, 电荷转移过程中, 对体系二阶NLO系数贡献较大的是配体内电荷转移(ILCT)和配体间电荷转移(LLCT)跃迁, 羰基引入后配体到金属的电荷转移(LMCT)使配合物[Ru^II(CO)₅L]²⁺比对应的配合物[Ru^II(NH₃)₅L]²⁺的β值增大约7倍.     

苯乙烯基-β-萘噻唑染料电子光谱的含时密度泛函研究

对苯乙烯基-β-萘噻唑染料系列用量子化学密度泛函方法(DFT)在B3LYP/6-31g水平上进行了几何构型全优化, 探讨了苯环对位上不同的取代基CH₃, OCH₃, N(CH₃)₂, 3,4-OCH₂O, NO₂等对分子电荷转移、前线轨道能量和电子光谱等性质的影响规律, 在此基础上采用含时密度泛函方法(TD-DFT)计算了分子第一激发态的电子跃迁能, 得到最大吸收波长λ_max. 计算结果表明, 上述5种取代基的引入, 均导致最大吸收波长红移. 与实验λ_max结果相比, 理论计算最大相对偏差为0.0501, 最小相对偏差为0.0085.     

非血红素铁(III)活化氧分子反应的自旋轨道耦合和零场分裂

采用密度泛函理论对原儿茶酚3,4-双加氧酶(3,4-PCD)活化O₂分子的反应机理进行了探讨. 初始复合物, 六重态⁶1的超快形成主要归因于电子交换诱导系间穿越(EISC), Fe d_z:O₂ π^*(z)是主要的交换通道, 在Fe―O键长为0.2487 nm处, 交换重叠积分S_ij=ád_z α|π^*(z) β>=0.3758. 从六重态⁶1 形成四重态中间体⁴1, 有两种效应共存, 即电子交换耦合作用和自旋轨道耦合(SOC)作用, 且相互竞争. 计算结果表明, 自旋轨道耦合(SOC)作用起主导因素(SOC=353.16 cm^-1). 至于O―O键的解离主要取决于儿茶酚(PCA)最高占据分子轨道(HOMO)的电子转移, 非血红素酶的铁中心仅承担PCA向O₂电子转移的缓冲作用.²²     

含有共轭炔基的发光Pt(Ⅱ)配合物发光性质的密度泛函理论研究

本文利用密度泛函(DFT)和含时密度泛函(TDDFT)方法研究了一系列配合物Pt(ppy)(C≡C)_nPh(ppy=6-phenyl-2,2′-bipyridine n=1～6)的基态和激发态的电子结构和发射光谱。计算揭示,当(C≡C)_n链长n=1～3时,配合物1～3的磷光发射被指认为是 ³[π^*(ppy) → Pt(5d),π((C≡C)_nPh)](³LMCT/³LLCT)的混合电荷跃迁。而当n=4～6时,配合物4～6的磷光发射主要是来自于(C≡C)_nPh配体内部³ππ^*跃迁(³ILCT)和少部分的³LLCT微扰跃迁。通过分析前线轨道成份,可以预测当炔基链长n趋于∞时,电荷跃迁将完全发生在炔基链的π轨道之间。     

锂在共轭双键高分子中的电化学嵌入反应III. 锂嵌入聚噻吩的量子化学计算†

采用Gaussian软件和HF方法, 通过从头计算(ab initio)法选取4-31G基组计算锂离子嵌入聚噻吩过程中结构与结合能的变化关系. 发现噻吩聚合时主要生成三或四聚合物. 聚合物在Li原子(或Li^＋离子)嵌入后, 聚噻吩间距离明显变小, 同时发生电荷转移, 形成稳定嵌合物; 并使噻吩环的C-α—C-β键级变小. 同时, 研究了锂离子(或原子)嵌入后体系的HOMO, LUMO能级. 聚噻吩在嵌入锂离子时LUMO轨道能级变为负值, 成为电池反应得电子的正极. 而金属Li₂ 释放Li^＋后的Li^－的HOMO能级为＋0.7427 eV, 则成为给电子的负极. 由此, 可以完成由锂/聚噻吩在高氯酸锂电解质中组成的放电过程, 并提出嵌合键级概念用来表征锂在聚噻吩间的结合程度.     

两个具有强双光子荧光的有机硼化合物

以二米基硼为电子受体, 苯乙烯基噻吩为共轭桥, 合成了两个新的稳定的有机硼化合物: 反式,反式-2-二米基 硼-5-{2-[4-(2-噻吩乙烯基)苯基]乙烯基}噻吩(1)和反式,反式-1,4-二-[2-(5-二米基硼噻吩)乙烯基]苯(2). 前者为不对称结构的偶极分子, 后者为对称的A-π-A型四极分子. 对称性不同的化合物表现出不同的双光子吸收性质. 对于偶极分子1, 单双光子吸收达到的激发态能级接近, 而对于四极分子2, 双光子吸收达到的激发态则比单光子吸收所达到的激发态高出0.35 eV. 在波长为710到 900 nm范围的飞秒脉冲激光激发下, 化合物1和2在THF溶液中都可以发出很强的绿色上转换荧光 (1, λ_max＝505 nm; 2, λ_max＝513 nm). 用双光子荧光法测得A-π-A型化合物2在775 nm处的双光子吸收截面达1340 GM.     

Highly regioselective thiocarbonylation of conjugated dienes via palladium-catalyzed three-component coupling reactions

Three-component coupling reaction of conjugated dienes, thiols, and carbon monoxide affords an atom-economical thiocarbonylation of the dienes to give beta,gamma-unsaturated thioesters as the sole products. A catalyst system based on [Pd(OAc)(2)] and Ph(3)P showed excellent catalytic activity. The thiocarbonylation was performed under an atmosphere of carbon monoxide (400 psi) at 110 degrees C in CH(2)Cl(2) for 60 h. A wide variety of thioesters were synthesized in good to excellent yields from easily accessible starting materials. The reaction is believed to proceed via a eta(3)-allylpalladium intermediate. The thiocarbonylation, which is applicable to a wide variety of conjugated dienes, occurs in high regioselectivity, the latter dependent on the steric characteristics and stability of the eta(3)-allylpalladium complex.     

Silicon-containing formal 4π-electron four-membered ring systems: antiaromatic, aromatic, or nonaromatic?

Density functional theory calculations (B3LYP) have been carried out to investigate the 4π-electron systems of 2,4-disila-1,3-diphosphacyclobutadiene (compound 1) and the tetrasilacyclobutadiene dication (compound 2). The calculated nucleus-independent chemical shift (NICS) values for these two compounds are negative, which indicates that the core rings of compounds 1 and 2 have a certain amount of aromaticity. However, deep electronic analysis reveals that neither of these two formal 4π-electron four-membered ring systems is aromatic. Compound 1 has very weak, almost negligible antiaromaticity, and the amidinate ligands attached to the Si atoms play an important role in stabilizing this conjugated 4π-electron system. The monoanionic bidentate ligand interacts with the conjugated π?system to cause π-orbital splitting. This ligand-induced π-orbital splitting effect provides an opportunity to manipulate the gap between occupied and unoccupied π?orbitals in conjugated systems. Conversely, compound 2 is nonaromatic because its core ring does not have a conjugated π?ring system and does not fulfill the requirements of a Hückel system.     

Silicon‐Containing Formal 4π‐Electron Four‐Membered Ring Systems: Antiaromatic,Aromatic, or Nonaromatic?

Density functional theory calculations (B3LYP) have been carried out to investigate the 4π‐electron systems of 2,4‐disila‐1,3‐diphosphacyclobutadiene (compound 1 ) and the tetrasilacyclobutadiene dication (compound 2 ). The calculated nucleus‐independent chemical shift (NICS) values for these two compounds are negative, which indicates that the core rings of compounds 1 and 2 have a certain amount of aromaticity. However, deep electronic analysis reveals that neither of these two formal 4π‐electron four‐membered ring systems is aromatic. Compound 1 has very weak, almost negligible antiaromaticity, and the amidinate ligands attached to the Si atoms play an important role in stabilizing this conjugated 4π‐electron system. The monoanionic bidentate ligand interacts with the conjugated π system to cause π‐orbital splitting. This ligand‐induced π‐orbital splitting effect provides an opportunity to manipulate the gap between occupied and unoccupied π orbitals in conjugated systems. Conversely, compound 2 is nonaromatic because its core ring does not have a conjugated π ring system and does not fulfill the requirements of a Hückel system.     

Improving charge transport in poly(3‐hexylthiophene) transistors via blending with an alkyl‐substituted phenylene–thiophene–thiophene–phenylene molecule

A prototypical semiconducting bicomponent system consisting of a conjugated polymer, that is, poly(3‐hexylthiophene) (P3HT), blended with a small thiophene containing conjugated molecule, that is, an alkyl‐substituted bisphenyl‐bithiophene [phenylene–thiophene–thiophene–phenylene (PTTP)], has been used as an electroactive active layer in field‐effect transistors (FETs). The self‐assembly of this bicomponent system at surfaces has been studied at different length scales, from the nanoscale to the macroscale, and compared with the behavior of monocomponent films of PTTP and P3HT. The correlation between morphology and electric properties of the semiconducting material is explored by fabricating prototypes of FETs varying the relative concentrations of the two‐component blend. The maximum charge carrier mobility value, achieved with a few percent of PTTP component, is not simply due to a uniform dispersion of the molecules in the polymer matrix, but rather to the generation of very long percolation paths, whose composition and electrical properties can be tuned with the PTTP concentration. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012     

Reactivity of n-Butyllithium[sbnd]CH3OCH2CH2OLi System as Catalyst for Copolymerization of Styrene with 1,3-Butadiene

The reactivity of n-butyllithium-CH₃OCH₂CH₂OLi in toluene (System A) in styrene-butadiene copolymerization reaction was found to be similar to that of the catalyst system n-butyllithium-poly(propylene oxide), which formed copolymers containing more styrene units than the feed monomer ratio at early stage of polymerization. Metalation reaction of toluene to produce benzyllithium was observed to take place in System A. Relative reactivity of each of chemical species present in System A was measured in the reactiom with butadiene, styrene, and 1,1-diphenylethylene, in connection with initiation and propagation reactions of copolymerization. From this study a living end anion possessing larger conjugated system was concluded to be more reactive toward monomers possessing larger conjugated system.     

Synthesis of new aromatic (C17-C20)-locked side-chain analogues of calcitriol (1alpha,25-dihydroxyvitamin D(3))

The synthesis of four new analogues of calcitriol (1alpha, 25-(OH)(2)-D(3)) possessing aromatic and conjugated double bond units at the side chain are described. The triene system is introduced using the Lythgoe-Hoffmann La Roche convergent Wittig-Horner approach. The key steps in the preparation of the requisite upper fragments are the introduction of the side chain with the E-conjugated aromatic system and its photochemical conversion to the Z counterpart.     

荧光共轭聚合物在生物大分子检测中的应用*

共轭聚合物因其具有π-电子体系及共轭离域结构,一般都具有优异的发光性能,其发光强度和发射波长会随被检测化合物结构的不同而发生特异性响应,特别是在与被检测物相互作用过程中所产生电荷和能量能够沿共轭分子链进行有效传递,成倍放大这种作用,从而有效提高了检测灵敏度,这比相应的小分子化合物更具有优越性。目前共轭聚合物已被用于开发新型化学、生物传感器,尤其是在生物分子检测方面的应用得到迅速的发展。本文总结了近年来荧光共轭聚合物在生物传感方面的研究进展,主要讨论共轭聚合物在蛋白质、核酸及毒素检测中的应用。     

Synthesis and electronic properties of terthienyls β-substituted by (thienyl)cyanovinylene groups

Terthienyls functionalized at their two outer β,β′-positions by 2- and 3-(thienyl)cyanovinyl groups have been synthesized by basic condensation. The analysis of their electronic properties by UV-vis spectroscopy and cyclic voltammetry shows that the mode of derivatization affects essentially the LUMO level of the conjugated system.     

Electropolymerizable 2,2'-Carboranyldithiophenes. Structure-Property Investigations of the Corresponding Conducting Polymer Films by Electrochemistry, UV-Visible Spectroscopy and Conducting Probe Atomic Force Microscopy

Carborane-functionalized conducting polymer films have been electrogenerated in dichloromethane from the anodic oxidation of ortho- (1), meta- (3) and para-carborane (4) isomers linked to two 2-thienyl units. The corresponding electrochemical response was characterized by a broad reversible redox system corresponding to the p-doping/undoping of the polythiophene backbone, the formal potential of which increased in the order poly(1) < poly(3) < poly(4), from ca. 0.50 to 1.15 V vs Ag/Ag(+) 10(-2) M. From further UV-visible spectroscopy analysis, the optical band gap was estimated at 1.8, 2.0 and 2.2 eV for poly(1), poly(3) and poly(4), respectively. The more conjugated and electroconductive character of poly(1) is ascribed to a more planar conformation of the conjugated backbone resulting from an intramolecular β-β' cyclization reaction in the monomer, consequently yielding a fused conjugated polymer. Molecular modeling calculations using the DFT method support this hypothesis. The surface topography and maps of the conductive domains of the electropolymerized films were evaluated by conducting probe AFM. The three polymers exhibit fairly similar morphological characteristics and a surface roughness of ~2 nm. Current-voltage (I-V) characteristics of conducting AFM tip-carborane polymer-ITO junctions showed that poly(1) had the highest conductivity.     

Synthesis,Photophysical Properties of Tribranched Chromophores Based on 1,3,5‐Triazine Core and Different Electro‐donating End‐groups

Three two‐photon absorption (TPA) tribranched chromophores were successfully prepared, in which 1,3,5‐triazine is been as electron deficient core, 1,4‐phenylenedivinylene as conjugated bridge, 3,4‐ethylenedioxythiophene (EDOT) ( T1 ), N‐methylpyrrole ( T2 ) or triphenylamine ( T3 ) as electron‐donating end‐groups. Their photophysical properties were studied by absorption, one‐ and two‐photon fluorescence and TPA cross‐section determination. The nonlinear transmission (NLT) measurement in femtoseconds (fs) regime at 800 nm indicates that TPA cross‐section (₂ values of T1 , T2 and T3 with extended Π‐conjugated bridge are much larger than the corresponding chromophore T4 with a short length bridge, and TPA cross‐section of T1 with end‐groups EDOT exhibits a remarkable enhancement compared with T2 and T3 having the same length Π‐system. The chromophores T1 , T2 and T3 show also remarkable up‐converted luminescence and optical limiting activity.